1. Field of the Invention
The invention relates to pressure measuring devices in general and more specifically to pressure measuring devices for use in reading the pressure of automotive systems such as automobile air conditioning systems.
2. Description of Related Art
Automobile air conditioners use gaseous chemicals called refrigerants to cool air. In accordance with Gay-Lussac's Law, which is:P/T=P′/T′ where V is constant  (1)and where P=pressure, T=temperature, V=volume, as the pressure of a compressed gas increases, its temperature increases. Similarly, as the pressure of the gas decreases, the temperature of the gas decreases. In this manner, gas is compressed and then expanded, and air is blown over that portion of the system in which the gas is expanded, and thus the blown air is cooled. Such is the basic concept of most refrigeration and air conditioning systems.
Since the pressure of the refrigerant plays an integral part of how efficiently an air conditioning system functions (or if it functions at all), it is desirable to be able to check the pressure of the refrigerant in the air conditioning system to insure that sufficient refrigerant is present. If the system pressure is too low, there will not be sufficient gas to compress and then expand, and the resultant change in temperature will be decreased; the air blown over the cooled portion of the system will, in turn, not be cooled sufficiently. Because the system is subject to significant swings in temperature and frequent thermal cycling—owing both to the action of the air conditioner as well as from the heat of the engine,—joints have a tendency to expand and contract, and refrigerant can slowly leak out of a system over time. One must keep a vigilant eye on the refrigerant level in one's automobile air conditioner.
Typical automotive air conditioners are provided with a service port to allow for the addition of refrigerant and other chemicals as well as to allow a qualified mechanic to check the level of the refrigerant in the system. For example, as shown schematically in FIG. 5A, a professional mechanic would likely use a manifold set 200, having a low pressure gauge 210 coupled to port 212 and a high pressure gauge 220 coupled to port 214. Hose 230 is attached to port 212 at one end and to the low pressure service port 250 via connector 240 at the other end. This device is large, heavy, and expensive, and it is really only suitable for the professional mechanic.
There are, of course, many automobile owners who choose to perform routine maintenance on their vehicles themselves. This market is commonly referred to as the “do-it-yourself” market, for self-evident reasons. A number of products have been developed by the assignee of the instant invention that allow the do-it-yourselfer to perform maintenance on an automobile air conditioner safely and easily. Some examples are described in U.S. Pat. No. 6,089,032; U.S. Pat. No. 6,446,453; and U.S. Pat. No. 6,467,283, all to Trachtenberg, the teachings of which are all herein incorporated by reference. These products include methods and kits for changing an air conditioning system over from using R-12 to R134a and a kit for servicing an air conditioning system.
The servicing kit of U.S. Pat. No. 6,446,453 includes a unitary hose connection for servicing an automobile air conditioning system and is shown schematically in FIG. 5B. A first connector 316 is disposed at one end of hose 314 and is connectable with a low pressure service port 250 of an automobile air conditioning system, and a second connector 312 is disposed at the other end of hose 314 and is selectively connectable with both a pressure gauge 310 and a can tap valve (not shown). The can tap valve is attachable to a can of compressed refrigerant. When pressure gauge 310 is attached to second connector 312 and first connector 316 is attached to service port 250, the pressure of the refrigerant in the automobile air conditioning system can be measured. When the second connector is attached to the can tap valve, the compressed refrigerant in the can may be introduced into the automobile air conditioning system to thereby service the system. The hose connection, pressure gauge, can tap valve, and can of refrigerant may be packaged together in a kit.
While the above-described servicing system is quite useful for servicing an automobile air conditioner, it is still a little cumbersome to use if one only seeks to measure the pressure in the system. First, the pressure can only be read while the hose is connected to the service port; once the hose is removed, the pressurized gas leaves the hose and the gauge returns to zero. As a result, if one has trouble getting close enough to the pressure gauge in situ, one will be unable to remove the gauge and read the pressure. Second, removing the hose from the port will cause the pressurized gas to shoot out of the hose in whatever direction the hose is pointing at the time; the possibility exists for refrigerant and the associated oil to be sprayed onto the user's skin or in his eyes, in certain circumstances. If a user is not careful when using the servicing kit and removes the pressure gauge while the hose is still attached to the service port (or if the user attaches the hose to the service port without first attaching the pressure gauge), the refrigerant and oil will come shooting out of the system via the hose, invariably in the direction of the user. Thus, the servicing kit described is not quite “idiot-proof.”
There is a need for a pressure gauge to allow a typical consumer to measure the pressure in his automobile air conditioner easily and safely.